1. Field of the Invention
The present invention relates to a discharging tube and a discharging method thereof, in particular, to a cold cathode fluorescent tube.
2. Description of the Related Art
In recent years, portable information terminal units such as note type personal computers and palm top type personal computers have been widely used.
For display units of these portable information terminal units, liquid crystal display units have been used because of small size, light weight, and low power consumption. For the light source of the back-light of the liquid crystal display unit, a cold cathode tube has been used. To cause the cold cathode tube to emit light, a high AC voltage is required. Thus, with an electromagnetic converting type AC inverter transformer, a high AC voltage is generated and thereby the cold cathode tube emits light.
FIG. 1 is a schematic diagram showing a driving method of a conventional cold cathode tube.
In FIG. 1, a DC voltage of around 10 to 15V is supplied from a DC power supply 271 to an inverter circuit 272. The inverter circuit 272 converts the DC voltage supplied from the DC power supply 271 to a high AC voltage of around 1200V/50 kHz. The resultant high AC voltage is supplied to a cold cathode tube 273. When the high AC voltage is supplied from the inverter circuit 272 to the cold cathode tube 273, the cold cathode tube 273 discharges electricity and emits light.
However, in the conventional driving method of a cold cathode tube, a high voltage wiring line should be connected from the inverter circuit 272 to the cold cathode tube 273. Thus, the voltage supplied from the inverter circuit 272 leaks out through the static stray capacitance of the high voltage wiring line. Thus, the power consumption for driving the cold cathode tube increases. Consequently, when the cold cathode tube is used for the back-light of a portable information terminal unit, the service life of the battery of the portable information terminal unit becomes short.